DTC P0420: Bank 1 Catalyst System - Low Efficiency: Condition
WARNING: This page is about a different car, the 2002 Suzuki XL-7. However, it is still accessible from the selected car via links, so may be relevant.
DTC P0420 is set when value from Bank 1 Heated Oxygen Sensor (HO2S) No. 2 becomes close to value of Bank 1 HO2S No. 1. MIL is illuminated when Engine Control Module (ECM) detects malfunction during 2 consecutive drive cycles.